Pyrolysis of cellulosic material in concurrent gaseous flow



' A. K. ESTE-RER' 3,298,923 ,PYROLYSIS OF GELLULOSIC MATERIAL` v f INCONCUBRENT GASEOUS FLOW Originall Filed Nov. 22, 1963 Jan. 11, 1967 2Sheets-Sheet l minceur CDIIDENSER f naamw L 4 PHASE upum GAS

INVENTOR. K. ESTERER GAS ` HOLDER.

HQU ID ORGANIC PHASE United States Patent 3,298,928 PYRLYSIS FCELLULOSIC MATERIAL 1N CONCURRENT GASEGUS FLGW Arnulf K. Esterer,Longview, Wash., assignor to Weyerhaeuser Company, Tacoma, Wash., acorporation of Washington.

Original application Nov. 22, 1963, Ser. No. 325,660. Di-

vided and this application Jan. 18, 1966, Ser. No. 52l,280 i i 9 Claims.(Cl. 21H-6) This is a division of my copending patent application SerialNo. 3256'60, filed November 22, 1963 and now abandoned; y

. This invention relates to the pyrolysisof cellulosic material. Inparticular it relates to the pyrolysis of lignocellulose, especiallywood, by entraining sawdust or other small lignocellulose particlesiny aVVgaseous stream and moving the particles'concurrently with the streamthrough a reaction zone in whichvthe lignocellulose is converted touseful degradation products such as levoglucosan and y variouscarbohydratederived acids such as humic, saccharic and saccharinicacids.` 4 y Both` of these classes of degradation products haveimportant or potentially'importantcommercial applications.

Levoglucosan potentially is useful as a raw material for the large scaleproduction of plasticizers, explosives, propellants, surfactants,vplastics, resins, and other products.

The carbohydrate-derived acids potentially are useful as raw materialsfor use in the synthetic organic chemical industry, and also assubstitutes for citric acid in the foodstuff industry.

Both levoglucosan and thecarbohydrate-derived acids are of particularinterest economically since they are derivable from wood and otherlignocellulose materials at very low cost. Their production accordinglyaffords a possible commercial utilization and'eco'nomic upgrading ofwastey wood products such as sawdust, chipsand shavings.

Although both levoglucosan and the carbohydratederived acidstheoretically are obtainable in high yields by the cleavage oflignocellulose, in practice the yields resulting from the prior artpyrolytic procedures have been quite small for various reasons.

For example, the lignin content of the lignocellulose interferes withthe pyrolysis reaction, leading to the development of'interfering sidereactions. Under the conditions of the pyrolysis levoglucosan itselfpyrolyzes readily into simpler products, such as acetic acid, acetone,phenols, water carbon monoxide gas, and char. Undercertain conditionslevoglucosan repolymerizes into products of higher molecular weight. Itsisolation and purification are diflicult. Passage of the desiredpyrolytic products through a bed of char, which is one of the productsof the reaction, necessitated by some of the prior art procedures,induces the breakdown of the reaction products. It is ditiicult tomaintain the lignocellulose particles in uniform suspension in theentrained gaseous medium so that a uniform reaction and a uniformreaction product are obtained. Control of the process conditions isextremely diicult.

Accordingly, it is the primary purpose `of the present invention toprovide a practical process, and apparatus, for the pyrolytic conversionof cellulosic material, especially sawdust and other lignocellulosematerials into levoglucosan, carbohydrate-derived acids, and otherdesirable end products, at relatively low cost, using wood wastestarting materials such as sawdust, wood chips, shavings and sugar canebagasse.

The manner in which the foregoing and other objects of the invention areaccomplished will be apparent from P YICC the Vaccompanyingspecifications and claims considere together with the drawings,wherein:

FIGURE l is a schematic flow plan of apparatus which' may be employed inthe presently described pyrolysis of lignocellulose in concurrentgaseous flow;l and FIGURES 2-8, inclusive, are schematic views ofdifferent types of pyrolytic reactors which may be included in theapparatus `of FIGURE l, FIGURE 7 being a cross sectional view of thepyrolytic reactor of FIGURE 6, taken along line 7-7 of that figure. i

The process of the present invention'takes advantage of l the fact that,even though` the pyrolytic degradation of lignocellulose tolevoglucosanand carbohydrate-derived acids, and the further `degradationof these desired products into carbon monoxide rand yother undesirableend products occurs in a time period of but a few seconds, propercontrol of the reactionl to Afavor the production of the desiredproducts and minimizel the production of undesirable by-products maybeachieved bymoving the lignocellulose particles and entraining gasthrough the pyrolysis zone, in concurrent flow, at a high rate of speed.

Such a procedure has the primaryVV advantage of minimizing the. passageof the levoglucosan and carbohydratederived acids through a fixed bed ofchar. This, in turn, minimizes degradation of the levoglucosan andcarbohydrate-derived acids into carbon monoxide and other undesirableby-products.

Passage of the lignocellulose particles and gaseous entraining mediumthrough the reactor in 'concurrent flow also overcomes the other primarydifficulty attending the pyrolysis of lignocellulose, i.e. that offorming in the first instance a uniform feed, and maintaining such afeed throughout the duration of the reaction.

In concur-rent tlow, the sawdust or other lignocellulose particles maybe mixed with the gas accurately, maintained in suspension and inuniform mixture with the gas throughout the entire reaction periodwithout coalescence. As a result, cracking and degradation of thelevoglucosan and carbohydrate-derived acids are kept at a minimum, andhigh yields of these desired end products are obtained.

In its broadest aspect, the process of the present invention thuscomprises introducing small pieces of cellulosic material, particularlywood or other lignocellulose, and a gaseous medium in concurrent flowthrough a reaction zone where they are heated to a temperature of from600-1500 F. The particles are maintained at this ternperature for areaction period not exceeding 30 seconds.

There thus is` formed a pyrolyzed product comprising char,noncondensable gases and condensable gases, which include thelevoglucosan and carbohydrate-derived acids.

At the conclusion of -the brief reaction period, the gaseous and charproducts of the pyrolysis are removed `from the pyrolysis zone andcooled to a temperature which is above the condensing temperature of thecondensable gases.

Before or after cooling, the gaseous products are separated f-rom thechar. They then separately are cooled further, condensing thecondensable gases including the levoglucosan. The resulting gas phasethen is separated from the resulting liquid phase.

The liquid phase is made up of a non-aqueous phase and an aqueous phase.These are separated. 'The nonaqueous phase contains useful tars andphenolic bodies. The aqueous phase contains the desired end products,i.e. levoglucosan and the carbohydrate-derived acids. It may beprocessed by a selected one of several procedures for recovery of theseproducts in high yield.

In the alternative, the cooling of the pyrolyzed product may beaccomplished in a single step condensing the condensable gases,including the levoglucosan, and resulting in a liquid product admixedwith char. The non-,con-l densable gaseous component then is separatedfrom the resulting liquid and char product. The latter product separatesin a non-aqueous phase containing char, tars and phenolic bodies and anaqueous phase containing levoglucosan and carbohydrate-derived acidswhich may be recovered by a selected one of several processes.

The term, non-aqueous phase, as used herein and in the claims isunderstood not to exclude the presence of small percentages of aqueousliquids.

A variety of cellulosic materials may be employed as raw materials forthe presently described procedure. Such materials include cottonlinters, shredded pulp, sugar cane bagasse, cornstalks, corn cobs, treebark and, particularly, the wood of various species of trees. The latteradvantageously may be in the form of such waste wood products assawdust, wood chips, flakes and shavings, which are available in verylarge quantitites at *low cost and presently comprise waste by-productsof the lumber industry.

Before entraining it in the gaseous medium, the cellu losic raw materialis reduced in size to the form of small, suspendable pieces. Althought-he size `of the pieces is subject to some variation, a product whichwill pass a 4- mesh sieve, U.S. Sieve Series, is suitable for thepresent purpose. Where sawdust is the starting material, itadvantageously may be passed through -a screen in order to screen outany large splinters `or other large pieces which might interfere withthe processing of the material.

The moisture content of the starting material also desirably may becontrolled to a level of less than 5% by weight, based on the dry`weight of the starting material. This is desirable in o-rder to avoidthe economic loss which would result from vaporizing a large amount ofwater. It also is desirable in order to maintain the temperature withinthe reactor vat the necessary level.

The cellulosic material may be dried in any suitable manner, preferablyby air drying, or by suspending it in hot gas, to a moisture content offrom 2-5%.

Although a variety of gases may be employed for entraining thecellulosic particles, the one selected should be substantially free ofoxidizing effects under the pyrolytic conditions, non-explosive, andpreferably non-toxic. Suitable gases accordingly comprise nitrogen,carbon di-oxide, steam and product gas, i.e. the gaseous productresulting from the pyrolytic degradation of the cellulose material.

Of these, steam may be employed to advantage since it has a high heatcapacity and heats the raw material rapidly to the reaction temperature.Also, during the condensation of the condensable gases in the product,the steam is converted to water. This helps to complete the condensationof tar aerosols or smokes which are present in substantial proportionand which are difficult to condense. Still further, by controlling theamount of steam used as a carrier, the degree of dilution of the aqueousphase product may be controlled as `required for further processing.

It is preferred to use superheated steam rather than saturated steam.This is desirable to insure proper heating and also prevent excessivewater dilution of the product.

The non-condensable gaseous product of the pyrolytic reaction, i.e.product gas also may be employed t0 advantage as a carrier gas. Althoughthe composition of this gas is somewhat variable, it comprisespredominantly carbon dioxide, methane and small amounts of uns-aturatedhydrocarbons. These are produced in suicient quantity to serve as asuspending and entraining medium to lill the system completely, and tomake up any Igas losses.

The gaseous medium is preheated to a temperature sufficient to bring thecellulosic material to pyrolyzing temperature when it is mixed with thegas. Accordingly, it is preheated to a temperature which when it ismixed in the predetermined ratio with the solid particles of the raw 4-material will bring the particles to a temperature within the range of,broadly, from 600-l500 F.

The identity of the cellulosic material, the nature and capacity of thereact-or employed, the size of the suspendable pieces and the procedureby which the reaction products are processed, all determine theparticular gasto particle :ratio which is employed. Sulicient gas mustbe employed to suspend and transport the particles through theprocessing stages. On the other hand, if too high a proportion of gas isemployed, the procedure becomes uneconomical and it may become difficultto fractionate the products of the reaction.

In general, a satisfactory ratio is from 5 to 20 pounds of carrier gasfor each pound of oven dry cellulosic material.

The temperature prevailing within the reactor through which theparticles and gas are passed in concurrent flow is broadly from 60G-l500 F. A preferred reaction temperature, insuring the production ofparticularly high yields of levoglucosan, is from 700-1100 P.

Within the reaction zone, the ow of gas is regulated so as to produceconcurrent flow, i.e. flow together in the same direction, of the gasand suspended cellulosic particles. To accomplish this purpose, thevelocity of the gas stream is established within the reaction zone at alevel which exceeds the carrying velocity of the particles or, statedotherwise, at a velocity which exceeds the sedimentation velocity of theparticles. The gas velocity thus necessarily is quite high, being of theorder' of from 200G-8000 feet per minute, or even higher.

The arrangement within the reactor is such that the gaseous stream doesnot traverse a fixed bed of char with consequent degradation of thepyrolytic products. However, the arrangement and dimensions of the bed,as well as the speed of flow of the gas may be varied so as to balanceor suspend the particles momentarily in their passage through thereactor as required to continue their pyrolysis to the desired degree.As pointed yout hereinafter, this lends llexibilty to the system in thatparticles of mixed size may be processed, the passage of the larger,heavier particles through the reactor being interrupted pending theirconversion to lighter particles by the pyrolytic process.

By adjusting the gas flow rate, the exposure of the pyrolysis gases tohigh temperature is kept at a minimum, since they are swept from thereactor substantially as soon as they are formed. It thus is possible tosecure a time-at-temperature of the particles not exceeding 30 seconds,preferably not exceeding l0 seconds, the selected time being dependentprimarily upon the particle size and the temperature of pyrolysis. Thisis in sharp contrast to the old wood carbonizing techniques whichrequired many hours to complete.

Excessive char formation and minimizing the occurrence of secondaryreactions of decomposition or repolymerization of the levoglucosan, areprevented by maintaining the reaction time at a relatively low value. Inother words, sweeping the levoglucosan and other pyrolysis products fromthe reaction zone with the concurrently flowing gas after an exposuretime of but a few seconds, favors the conversion of the cellulose tolevoglucosan and prevents the further decomposition or change of thatproduct into unwanted by-products.

The product leaving the reaction zone contains broadly from l050% byweight char, from l5-60% xed noncondensable gases and from 20-65%condensable gases.

In the first stage of its processing, the mixture is passed through asolid-gas phase separator which may comprise a cloth tilter, acentrifuge or, preferably, a cyclone separator. During the separationthe separator is kept hot at a temperature above the condensationtemperature of the condensable gases in order to eliminate plugging ofthe separator elements withtar, and to prevvent loss of valuablevolatile products. Also, the dwell time in the hot separator is kept ata minimum, i.e. not

over a` few seconds, in order to prevent or minimize decomposition ofthe levoglucosan and carbohydrate-derived acids.

The solid product leaving theA separator comprises the char. This hasaixed carbon content of the order of 65-90% by weight in Vthe event thatthe conversion of the cellulosic starting materialv in the reactor hasbeen substantially complete. The xed carbon level of the char may bevaried by control ofthe operating variables, however, asideterminedbythe end use to which the product is to be p'ut. When `it is to be usedas absorption charcoal, it should be substantially free from tar.However, if it is to'ibe applied to `theI manufacture of fuel briquets,a lower carbon content is permissible, the increased tar contentyserving as an adhesive to bind the char particlesinto briquets.

The gaseous product leaving the ysolid-gas phase separator includes bothcondensable and non-condensable gases. Itn accordingly is -passd`througha condenser unit which may comprise a battery of individual,water-cooled, corrosion-resistant condensers connected in series. Asnoted above, Where superheated steam comprises the carrier gas, thesteam condensed into water at this stage serves to dilute thecondensedproduct to ia'degree which rendersrit suitablefor further processing.

As products of the condensing stage there are obtained a gaseousproduct, i.e`. product gas, and a liquid product. v

The product gas is obtained in a yield of -60% by weight, b a'sed on thedry starting material. It contains carbon dioxide, methane4 ,and othersaturated hydrocarbons, and a small amount of ethylene and otherunsaturated-hydrocarbons. Its exact composition varies,depending'primarily upon the temperature of the pyrolysis.

The product gas thus obtained may be used, after washing out its carbondioxide content with lime, as a raw material for carbon monoxidesyntheses. In the alternative, the product gas'may be employed withoutfractionation or further treatment .as the gaseous medium required forthe presently described pyrolysis.

The liquid product -asy irst obtained, is a brown 4fluid which separatesupon standing into a non-aqueous organic phase and an aqueous orWater-soluble-organic phase. The `two phases may be separated byprocessing the total liquid product in a liquid product separator ofsuitable construction. This results in the separation of a. non-aqueousphase fraction comprising about -60% `by weight of the total liquidproduct and an aqueous phase fraction comprising from 4080% of the totalliquid product.

The non-aqueous organic phase consists primarily of tars and phenolicbodies such las guaiacol, the cresols, creosol, and the higher phenols.y They are obtained in a yield of from 4-3S% by weight, based on the dryWeight of the starting material, and may bealpplied to the variousindustrial uses to which such materials are applicable either as a grossproduct or after fractionation.

` The aqueous phase is made up of a solid component dissolved in anaqueous liquid. The aqueous liquid comprises principally water, butincludes also appreciable quantities of formic acid, acetic acid, andsoluble phenols.

The solid component of the aqueous phase, which represents from l4-38%by weight'of the dry cellulosie material, consists of variouscarbohydrate fragments in cluding levoglucosan and thecarbohydrate-derived acids such as humic, saccharie and saccharinicacids, or other cleavage products of sugars. These products may beseparated from the aqueous liquid in which they are dissolved, and usedas a gross product. they may be separated from each other by suitabletechniques such as selective solvent extraction and then applied totheir various indicateduses.

Suitable .apparatus for carrying out 'the foregoing sequenceof-opera'tions is lillustrated schematically in FIG- URE l.

In the alternative,

As indicated in that figure, sawdust or other cellulosic particles arefed from a storage bin 10 through conduit 12 into a drier 14, `wheretheir moisture content is adjusted to a selected level of, for example,less than 5% :by Weight.v The drier is heated by hot gas generated ingas heater 16 passing via conduit 18 into the drier from which it isexhausted through stack 20.

The dried particlesleave thepdrier through conduit 22 and are valved bymetering valve 24 into la conduit 26. Here they are mixed withthegaseous medium, for example, hot, recycled, product gas.

a Next the lpredetermined mixture of particles and gas is passed inuniform, measured flow into la reactor indicated generally at 28. vThereactor may assume various forms, illustrated in FIGURES 2-8 to bediscussed hereinafter.

Afterna' brief residence time in the reactor, the hot reactionmixture'comprising char, condensable gases and non-condensable gases ispassed into a solid-gas separator which, in the illustrated form of theinvention, Vcomprises a cyclone'separator 30. Here the char is separatedand gravitates into a receiver 32. v Thejhot gases exit from the cyclonevia conduit 34 and next are passed through a condenser 36. Thiscondenses the condensable gas component ofthe gaseous mixture. A

The resultant two'phases comprising the liquid phase including thecondensed condensable gases and the gas phase comprising thenon-condensabl'e g-ases is passed into aliquid-g-as separator 38. y

The non-condens'able' gases including the carbon dioxide, hydrocarbonand other gases leave the seperator through conduit l40. Part of themare withdrawn through conduit 42 and are received in a gas holder 44.Another part passes through conduit 46 into gas compressor 48 whichcompresses them and passes them through conduit 50 andvalve 52 intorecycle gas heater 16.

Here, as explained above, the gases are heated to a temperaturepredetermined to raise the particles to the reaction temperature, andpassed into conduit 26 where they are mixed with solid cellulosicparticles and, together with them, recycled into reactor 28;

The liquid product emanating from gas separator 38 passes through a pipe54 into a liquid product separator 56. l i In 4this separator, theorganic phase comprising phenolic bodies, tars and the like, isseparated from an aqueous phase containing water-soluble organiccomponents of the reaction. Y

The organic phase is withdrawn from the separator through line 58 whichincludes a pump 60. This transfers the organic phase to a receiver 62where it is stored preliminary to its future disposal.

The aqueous phase, including the levoglucosan, carbohydrate-derivedacids, and other desired pyrolytic degradation products is withdrawnfrom separator 56 via line 64 whichincludes a pump`66. It is stored in atank v6l; preliminary to its being conducted into a'sequence of-suitable apparatus and procedures designed to separate the organicconstituents of the aqueous phase from each other. A particulardesirable method of `accomplishing the desired separation of the organicconstituents comprises the subject matter of my co-pending 4applicationentitled Separating Levoglucosan and Carbohydrate-Derived Acid FromAqueous Mixtures Containing The Same--By Solvent Extraction. In thisrnanner levoglucosan may be separated from the carbohydrate-derivedacids for application to their various uses. l

As indicate-d above,` pyrolytic reactor 28 may assume a diversity offorms and congurations depending upon such considerations as theidentity of the starting material, the temperature and other. reactionconditions and the identity of the pyrolytic product desired.

The reactor 28a illustrated in FIGURE 2 represents the simplest design'.4It comprises simply a substantially vertical tube having a substantiallengt-h, for example a length of `as much as 120 feet. Its overallheight may be reduced by including it, or 'by bending it slightly,thereby inducing a sweeping action of the carrier gas. Its length may bedetermined in part by the temperature employed and the reactor dwelltime required. In other words, the length of t-he reactor may varydirectly with the desired dwell time and inversely with the reactiontemperature.

The reactor 2817 illustrated in FIGURE 3 is of the updraft-downdrafttype wherein updraft and downdraft zones are provided. Such anarrangement is possible because in prolysis by concurrent flow thecarrier gas velocity is greater than the sedimentation velocity of thelignocellulose particles, so that they are swept rapidly through boththe updraft and downdr-aft portions of the apparatus. This lends to theapparatus the advantages of accurate control of the brief pyrolysisinterval. It also conserves space.

The downdraft-updraft reactor 28C of FIGURE 4 is the inverse of thereactor shown in FIGURE 3. In the rst, or downdraft section, the carriergas Velocity can be reduced so that it isbarely larger than the particleacceleration by gravity. In the terminal updraft section, the carriergas velocity is sufficient to sweep the lighter char particles out ofthe reactor. In the intermediate or transitional section of the reactor,the larger particles which have not been decomposed by pyrolysissufliciently to be swept out of the reactor in the updraft section areretained briey until their pyrolysis is complete. This form of theapparatus thus affords exceptional control of the operating variablesand also lends flexibility to it in that it enables .accommodation ofthe apparatus to particles of varying size.

The spiral form of reactor 28d illustrated in FIG- URE 5 may assume theshape of a coiled pipe, or of a cylindrical shell containing a spiralvane 102 in the manner illustrated. Such an apparatus reduces theoverall height requirement while keeping unchanged the length of thereaction zone.

The reactor 28e of FIGURE 6 is designed to occupy minimum space while atthe same time reducing the turbulence which might be present in areactor vof substantial diameter. It comprises a cylindrical shelldivided into a multiplicity of vertical passageways by a network ofinterlaced partitions 104. In it, the carrier gas and particles. to bepyrolyzed are swept rapidly upwardly through the passageways inupdraft,rcor1current ow, into the separator 30.

The reactor 28f of FIGURE 8 embodies a temporary particle suspensionprinciple. The reactor comprises a cylindrical shell of substantialdiameter and without partitions. The carrier gas velocity is maintainedsuiciently high to keep the particles suspended in the lower part O fthe reactor. After part of the reaction time has elapsed, for example, asecond or two, the pyrolyzed char particles have become light enough to`be swept out by the carrier gas. There thus is a temporary interruptionof the concurrent ilow sufficient to eifectuate the pyrolysis to thede,- sired degree.

The apparatus of FIGURE 8 accordingly contains a built in retardingfeature which retards the flow of the particles and gives superiorcontrol of the reaction. In addition, the reactor will accommodateparticles of nonuniform size since the larger the particles, the longerthey are retained until they are rendered light enough by pyrolysis tobe swept out of the reactor. Still further, the height of thereactorpmay be maintained at `a minimum.

The application of the invention to the manufacture of levoglucosan fromwood is illustrated in the following examples:

EXAMPLE 1 Oven dry Douglas fir sawdust having a mesh size of 4, U.S.Sieve Series, was pyrolyzed in a pyrolytic reactor of the typeillustrated in FIGURE 8, included in a systemsuch as is `illustrated-inFIGURE 1. The reactor consisted of a vertical, 4hollow tube provided atits lower end with an inlet duct and at its upper end with an outletduct communicating with a cyclone separator for separating the char fromthe gaseous product of the reaction.

The feed sawdust was mixed with heated product gas in the ratio of 7pounds lof gas per pound of sawdust. The sawdust in this mixture thenwas fed to t-he reactor at a flow rate of 12.5 pounds per hour.

The temperature within the reactor was 750 F. The pressure w-asmaintained at atmospheric pressure. The velocity of the carrier gas wasapproximately 3000 ft./ min. so as to maintain the particles insuspension in the chamber until their pyrolysis had been effected to thedesireddegree, whereupon the relatively light particles of char wereconveyed out of the reactor into the cyclone separator. Theaveragcresidence time ofthe gaseous components within the reactor was twoseconds.

The product lefuent from the reactor comprised 20% char, 64.8% condensedflow gases and 15.2% non-condensable gases, these representingquantities of 2.5, 8.1 and 1.9 pounds per hour respectively.

The gases leaving the cyclone next were passed through a condenser andthence into a liquid-gas separator, which separated the condensablegases from the non-condensable gases. The latter in part were vented andin part recycled. The former were passed to a liquid product separatorwhich separated them into a non-aqueous phase, and an aqueous phase.

The non-aqueous organic phase represented 12.8% of the starting materialor `1.6 pounds per hour. The aqueous phase represented 52% of thestarting material or 6.5 pounds per hour. It contained 1.5 pounds perhour of levoglucosan representing 12.0% of the starting ma terial. TheWater present represented 14% of the starting material, or 1.75 poundsper hour.

Theraqueous phase was processed using the solvent extraction procedureof my -co-pending -application mentionedpreviously, resulting in alyield of 1.4 pounds per hour of levoglucosan representing 11.2% of theoriginal starting material.

EXAMPLE 2 Shredded'wastepaper (newsprint) was pyrolyzed in a pyrolyticreactor and system as described in Example 1 under similar conditions`with the following exceptions: the feed w-astepaper was mixed withheated product gas in the ratio of 7.2 pounds of gas per pound ofwastepaper, the ilow rate to the reactor was 8 pounds of wastepaper perhour and the temperature within the reactor was maintained at 1100 F.

The product effluent from the reactor `comprised 31.7% char, 30.3%condensed flow gases and 38.0% non-condensable gases, these representingquantities of 2.54, 2.42, and 3.04 pounds per hour respectively.

`The gases leaving the cyclone next were processed as described inExample 1. An aqueous phase was obtained representing 13.9% of thestarting material or 1.11 pounds perv hour. Upon processing using thesolvent extraction system referred to in Example 1, a yield of 0.19pound per hour of levoglucosan was obtained representing 2.4% of theoriginal starting material.

EXAMPLE 3 Cotton linters were pyrolyzed in a pyrolytic reactor andsystem as described in Example 1 under similar conditions with thefollowing exceptions: the feed cotton linters were mixed with the heatedproduct gas in the ratio of 6.4 pounds of gas per pound of cottonlinters and the flow rate to the reactor was 9 pounds of cotton lintersper hour.

The velocity of the carrier gas was adjusted to approximately 4000 feetper minuteiresulting in anaverage rcsidencetime for thegaseouscomponents within the reactor of 1.5 seconds.

The product eluent from the reactor comprised 16.6% char, 67% condensedow gases and 15.5% non-condensable gases, these representing quantitiesof 1.5, 6.0, and 1.4 pounds per hour, respectively.

The gases leaving the cyclone next were processed as described inExample 1. An aqueous phase was obtained representing 56.6% of thestarting material or 5.1 pounds per hour. Upon further processing usingthe solvent extraction system referred to in Example 1, a yield of 2.46pounds per hour of levoglucosan was obtained representing 27.3% of theoriginal starting material.

Having thus described the invention in preferred embodiments, what isclaimed as new and desired to protect by Letters Patent is:

1. A process for the pyrolytic degradation of cellulosic material whichcomprises:

(a) introducing small pieces of cellulosic material :and

a stream of heated gas substantially free of oxidizing effects into areaction zone,

(b) moving the pieces and the entraining hot gaseous medium inconcurrent flow through the reaction zone,

(c) maintaining the pieces in the reaction zone at a temperature of600-1500 F. thereby forming -a reaction product comprising char,condensable gases and non-condensable gases,

(d) removing the reaction product from the reaction zone after aresidence time not exceeding 30 seconds,

(e) rapidly cooling the reaction product,

(f) separating the resulting condensate of condensed gases and ycharfrom the non-condensable gases and (g) separating from the condensatethe selected pyrolytic degradation products of the cellulosic material.

2. The process of claim 1 wherein the cellulosic pieces are maintainedin the reaction zone at a temperature of 750 F. and the reaction productis removed after a residence time not exceeding 10 seconds.

3. The process of claim 1 wherein the cellulosic pieces and gaseousmedium are moved through the reaction zone in substantially continuous,updraft concurrent ow.

4. The process of claim 1 wherein the cellulosic pieces and gaseousmedium are moved through the first part of the reaction zone in updraft,concurrent flow and through the second part of the reaction zone indowndraft, concurrent ow.

5. The process of claim 1 wherein the reaction zone is provided indowndraft, updraft and intermediate transition zones 'and wherein thecellulosic pieces and gaseous medium are moved in concurrent flow athigh velocity through the downdraft zone and at a lesser velocitythrough the updraft zone, the pieces being held in the transition zonefor a time duration predetermined to reduce by pyrolysis their weight toa level at which they are moved by the gaseous medium through theupdraft zone.

6. The process of claim 1 wherein the velocity of the gaseous mediumrelative to the cellulosic pieces is maintained at a level suicient tosuspend the pieces momentarily in the reaction zone, whereupon theirweight is reduced by the pyrolytic operation occurring therein, thegaseous medium velocity thereupon being sufficient to sweep theparticles from the reaction zone in concurrent updraft ow.

7. The process of claim 1 wherein the cellulosic pieces and gaseousmedium are moved in spiralling concurrent flow through the reactionzone.

8. The process of claim 1 wherein the cellulosic material compriseslignocellulose.

9. The process of claim 1 including the step of separating the char fromthe reaction product prior to cooling the resulting gaseous reactionproduct.

References Cited by the Examiner UNITED STATES PATENTS 1,941,809 1/ 1934McKee 48-223 2,289,917 7/ 1942 Lambiotte 201-34 2,623,011 12/ 1952 Wells201-31 MORRIS O. WOLK, Primary Examiner.

JAMES H. TAYMAN, IR., Assistant Examiner.

1. A PROCESS FOR THE PYROLYTIC DEGRADATION OF CELLULOSIC MATERIAL WHICHCOMPRISES: (A) INTRODUCING SMALL PIECES OF CELLULOSIC MATERIAL AND ASTREAM OF HEATED GAS SUBSTANTIALLY FREE OF OXIDIZING EFFECTS INTO AREACTION ZONE, (B) MOVING THE PIECES AND THE ENTRAINING HOT GASEOUSMEDIUM IN CONCURRENT FLOW THROUGH THE REACTION ZONE, (C) MAINTAINING THEPIECES IN THE REACTION ZONE AT A TEMPERATURE OF 600-1500*F. THEREBYFORMING A REACTION PRODUCT COMPRISING CHAR, CONDENSABLE GASES ANDNON-CONDENSABLE GASES, (D) REMOVING THE REACTION PRODUCT FROM THEREACTION ZONE AFTER A RESIDENCE TIME NOT EXCEEDING 30 SECONDS, (E)RAPIDLY COOLING THE REACTION PRODUCT, (F) SEPARATING THE RESULTINGCONDENSATE OF CONDENSED GASES AND CHAR FROM THE NON-CONDENSABLE GASESAND (G) SEPARATING FROM THE CONDENSATE THE SELECTED PYROLYTICDEGRADATION PRODUCTS OF THE CELLULOSIC MATERIAL.